The effect of herring gulls on the vegetation of the Isle of May

Summary

Herring and lesser black-backed gulls have increased dramatically on the Isle of May from a single pair in 1907 to an estimated 39,000 birds in 1972. This increase in numbers and the resulting extension of the breeding colony to cover a high proportion of the island area has resulted in drastic vegetation changes. The vegetation of the island was assessed and mapped in 1972, and a comparison with previous assessments of 1936 and 1957, when there were far fewer gulls than at present, reveals that the thrift heath which once covered most of the island's periphery has been replaced by plant communities dominated by Holcus lanatus and annual species—particularly Stellaria media. These and other changes which have occurred in the intervals are described, and an attempt is made to explain how gull activities are responsible.